1. Field of the Invention
The present invention generally relates to a safety syringe, and more particularly to a safety syringe which has a vacuum generating device.
2. Description of the Prior Art
FIG. 1 shows a perspective view of a conventional syringe. The conventional syringe 100 includes an outer syringe barrel 110, a rod 120, and a needle unit 130. The needle unit 130 is fixed on the front end of the outer syringe barrel 110 by screw thread. The rod 120 has a plug portion 121. The plug portion 121 is in air-tight contact with the inner wall of the outer syringe barrel 110. When performing an injection process, the rod 110 is pushed toward the front end of the outer syringe barrel 110 by a user, and the medical solution within the syringe 100 can flow through an opening of the needle unit 130. After the injection process, the needle unit 130 should be enclosed with a needle sheath by the user manually. However, it is possible that the user may be stuck by the needle unit 130, and infection risk of the user is increased. Therefore, safety syringes with needles that can be retrieved automatically have been provided to prevent the user from risk of infection.
Generally, the needles of the safety syringes are retrieved automatically by low pressure. The low pressure is sealed within the safety syringe during the making process of the safety syringe. Before the safety syringe is used, the air is sucked gradually into the safety syringe, and the low pressure sealed within the safety syringe is also decreased gradually. Finally, the needles of the safety syringes may fail to be retrieved automatically because the low pressure is insufficient.
For the reason that there are disadvantages of the prior art as mentioned above, a need has existed to propose a novel safety syringe. The safety syringe has a vacuum generating device that is able to generate enough low pressure to prevent the situation where the needle of the safety syringe may fail to be retrieved automatically because of the low pressure not being adequate.